For people with normal, regular (sinus) heart rhythm, the interval between heart beats is relatively constant. However, many others (like me) sometimes experience irregular heartbeat rates, and the time interval between beats varies. There can be many causes of irregular heartbeat, and it is useful to be able to monitor the degree of irregularity under various conditions, and sometimes helpful to look for patterns in the rhythm. Using an Arduino Nano, an Easy Pulse sensor, and Processing I have built a heartbeat monitor that plots the statistics of the heartbeat inter-beat interval (IBI) showing the distribution of IBI's over a sequence of beats. This gives measure of degree of irregularity. The system also allows listening to a speeded-up replica of the heart rhythm to detect rhythmic patterns. The Arduino and Processing sketches are derived from those posted for the PulseSensorAmped sensor, since they were a better fit to the application than the Easy Pulse variants.

I found that it's important to either run the sensor from a separate power supply or clean up the output from the USB- supplied Nano 5V pin. I used a 3.3V regulator to clean up the Nano 5V output and ran the sensor at the reduced voltage. A single earbud driven by a Nano digital pin through a 330 ohm resistor allows listening to an accelerated version of the heart rhythm for a sequence of 100 pulses.

I see that the attachment doesn't open without downloading. Please download it for pictures and examples or go to http://www.potomacmeso.com/heart-rhythm-monitor.html for more information on hardware and Arduino and Processing sketches.